1. Field of the Invention
The present invention relates to an image blur prevention apparatus for preventing an image blur caused by hand vibration or the like in a camera, optical equipment, or the like.
2. Related Background Art
In currently available cameras, all operations important to take a picture, e.g., exposure and focus control, are automatically determined. Therefore, even an unskilled user rarely fails in a photographing operation.
Further, since a system for preventing influence of hand vibration of a photographer on a camera has recently been studied, there are few or no factors causing a failure in a photographing operation by the photographer.
The system for preventing hand vibration will be described here in brief.
In general, hand vibration of the photographer using the camera in a photographing operation falls within a vibration range of 1 Hz to 12 Hz. According to a basic concept of taking a picture without any image blur even when hand vibration is created by the photographer in a shutter release operation of the camera, it is necessary to detect camera vibration (fluctuation) caused by the above hand vibration and displace a correction lens in accordance with the detection value. In order to achieve the above object (i.e., to take a picture without any image blur even with camera vibration), first of all, camera vibration must be accurately detected, and secondly, a change in optical axis due to hand vibration must be corrected.
In principle, detection of this vibration (camera vibration) can be performed by mounting a vibration sensor and a camera vibration detecting means in a camera. The vibration sensor detects an angular acceleration, an angular velocity, an angular displacement, and the like. The camera vibration detecting means electrically or mechanically integrates output signals from the sensor to output an angular displacement. Image blur suppression can then be performed by driving a correction optical apparatus for offsetting the photographic optical axis on the basis of the detection information.
A blur prevention system using a vibration detecting means will be described here with reference to FIG. 38.
FIG. 38 shows an example of a system for suppressing an image blur resulting from vertical camera vibration (fluctuation) 81p and lateral camera vibration (fluctuation) 81y in directions 81 indicated by the arrows in FIG. 38.
Referring to FIG. 38, the system includes a lens barrel 82 and vibration detecting means 83p and 83y for respectively detecting a vertical camera vibration and a lateral camera vibration in vibration detecting directions 84p and 84y. It also includes a correction optical apparatus 85 (coils 87p and 87y for giving a thrust to the correction optical apparatus, and position detection elements 86p and 86y for detecting the position of the correction optical apparatus). The correction optical apparatus 85 has a position control loop to be described later. The correction optical apparatus 85 is driven by using outputs from the vibration detecting means 83p and 83y as target values, thereby stabilizing an image surface 88.
FIG. 39 is an exploded perspective view showing the structure of a suitable blur correction apparatus (as will be described later in detail, which is constructed of a correction means, means for supporting and engaging the correction means, and the like). The structure will be described below with reference to FIGS. 39 to 48.
Three backside lugs (one lug is hidden) of a base plate 71 (also shown in an enlarged view of FIG. 42) are fitted or inserted in a lens barrel, not shown, and a known barrel roller or the like is fixed to the lens barrel by tightening screws into holes 71b. 
A bright-plated second yoke 72 as a magnetic material is fixed to the base plate 71 by tightening screws into holes 71c through holes 72a. Permanent magnets (shifting magnets) 73 such as neodymium magnets are magnetically absorbed on the second yoke 72. The permanent magnets 73 are respectively magnetized in directions indicated by the arrows 73a in FIG. 39.
A correction lens 74 is fixed to a support frame 75 (see an enlarged view of FIG. 43) by means of a C ring or the like, and coils 76p and 76y (shifting coils) are forcibly pressed in the support frame 75 (FIG. 43 shows a non-adhesive state). Light-projecting elements 77p and 77y such as IREDs are also adhered to the back face of the support frame 75, and light emitted from the light-projecting elements is incident on position detecting elements 78p and 78y, such as PSDs, to be described later, through slits 75ap and 75ay respectively.
Support balls 79a and 79b each having a round tip, made of POM (polyacetal resin) or the like, and a charge spring 710 are inserted into holes 75b (provided in three places) of the support frame 75 (also see FIGS. 40, 41A and 41B). The support ball 79a is heat-caulked and fixed to the support frame 75 (where the support ball 79b is slidable in a direction to project from the hole 75b against the spring force of the charge spring 710).
FIG. 40 is a transverse sectional view of the blur correction apparatus after assembly. Referring to FIG. 40, the support ball 79b, the charge spring 710 previously charged, and the support ball 79a, are inserted into the hole 75b of the support frame 75 in this order (where the support balls 79a and 79b have the same shape). The surrounding edge 75c of the hole 75b is heat-caulked to prevent the support ball 79a from coming off.
FIG. 41A is a sectional view of the hole 75b taken on a line perpendicular to FIG. 40, and FIG. 41B is a plan view as seen from the direction indicated by the arrow 79c in FIG. 41A. Reference labels A to D in FIG. 41A denote respective depths of regions labeled by A to D in FIG. 41B.
Since the rear ends of vane portions 79aa of the support ball 79a are received in the region with the depth surface A, and movement of the vane portions 79aa is restricted by the depth surface A, the support ball 79a is fixed to the support frame 75 by heat-caulking the surrounding edge 75c. 
On the other hand, since the tips of vane portions 79ba of the support ball 79b are received in the region with a depth surface B, the support ball 79b is prevented from passing through the hole 75b in a direction indicated by the arrow 79c due to the spring force of the charge spring 710.
After the correction apparatus has been assembled, since the support ball 79b is received by the second yoke 72 in the manner shown in FIG. 40, the support ball 79b is prevented from getting out of the support frame 75 even when the surface B is not provided. However, the surface B as the region to prevent the support ball 79b from passing through the hole 75b is provided for ease of assembly.
Since drilling of the hole 75b does not need any complicated internal sliding die even when the support frame 75 is made up by molding, and simple split-half dies can be used for molding the support frame 75, the shape of the hole 75b of the support frame 75 shown in FIGS. 40, 41A and 41B can be set with high dimensional accuracy.
Thus the support balls 79a and 79b can be made up as the same parts, so that parts costs can be reduced without any assembly error. This is effective in parts control.
A material such as fluorine base grease is applied to a bearing portion 75d of the support frame 75. An L-type shaft 711 (made of non-magnetic stainless steel) is then inserted in the bearing portion 75d (see FIG. 39), with the other end of the L-type shaft 711 being inserted into a bearing portion 71d formed on the base plate 71 (after applying grease as well). After that, the support balls 79 provided in three places are put together on the second yoke 72, and the support frame 75 is mounted in the base plate 71.
Next, positioning holes 712a (provided in three places) of a first yoke 712 shown in FIG. 39 are fitted with respective pins 71f (provided in three places) of the base plate 71 shown in FIG. 42. The first yoke 712 is received by receiving surfaces 71e (provided in five places) as also shown in FIG. 42, and magnetically coupled to the base plate 71 (by the magnetic force of the permanent magnets 73).
Thus the back face of the first yoke 712 strikes or contacts the support ball 79a, and the support frame 75 is held between the first yoke 712 and the second yoke 72, thereby positioning the optical axis.
The contact surfaces of the support balls 79a and 79b with the first yoke 712 and the second yoke 72 are also covered with grease so that the support frame 75 can slide on the plane perpendicular to the optical axis with respect to the base plate.
In other words, the L-type shaft 711 supports the support frame 75 such that the support frame 75 can slide only in directions indicated by the arrows 713p and 713y with respect to the base plate 71, thereby restricting or controlling the relative rotation (rolling) of the support frame 75 to rotate about the optical axis with respect to the base plate 71.
A play in fitting the L-type shaft 711 in the bearing portions 71d and 75d is set larger in the optical axis to prevent duplicative fit with the restrictions in the optical axis caused by holding the support balls 79a and 79b between the first yoke 712 and the second yoke 72.
The surface of the first yoke 712 is covered with an insulating sheet 714, and a hard substrate 715 having a plurality of ICs (position detecting elements 78p and 78y, an output amplification IC, a driving IC for coils 76p and 76y, and the like) is fixed to the w base plate 71 by fitting positioning holes 715a (provided in two places) with pins 71h (provided in two places) of the base plate 71 as shown in FIG. 42 and tightening screws into holes 71g of the base plate 71 through holes 715b and holes 712b of the first yoke 712.
The position detecting elements 78p and 78y are put in place with a tool and soldered on the hard substrate 715. A flexible substrate 716 is also mounted on the back face of the hard substrate 715 by heating and pressure-welding a surface 716a on an area 715c indicated by the broken line (see FIG. 39).
A pair of arms 716bp and 716by extend from the flexible substrate 716 in respective directions on the plane perpendicular to the optical axis. The arms 716bp and 716by are then caught by hook portions 75ep and 75ey (see FIG. 43), and terminals of the light-projecting elements 77p and 77y, and terminals of the coils 76p and 76y are soldered.
Thus the light-projecting elements 77p and 77y such as IREDs and the coils 76p and 76y are driven by the hard substrate 715 through the flexible substrate 716.
The arms 716bp and 716by of the flexible substrate 716 respectively have bend portions 716cp and 716cy (see FIG. 43). The use of elasticity of the bend portions reduces the load on the arms 716bp and 716by caused by movement of the support frame 75 on the plane perpendicular to the optical axis.
The first yoke 712 has a projection surface 712c patterned by rapping. The projection surface 712c directly contacts the hard substrate 715 through a hole 714a of the insulating sheet 714. On the side of the hard substrate 715, earth (GND: ground) pattern is formed on this contact surface. Thus the first yoke 712 is grounded by screwing the hard substrate 715 to the base plate 71 and is used as an antenna to prevent noise on the hard substrate 715.
A mask 717 shown in FIG. 39 is positioned by the pins 71h of the base plate 71 and fixed on the hard substrate 715 with adhesive double coated tape.
A through hole 71i for permanent magnets is opened through the base plate 71 (see FIGS. 39 and 42), and the back face of the second yoke 72 is exposed therefrom. A permanent magnet (locking magnet) 718 is incorporated in the through hole 71i and magnetically coupled to the second yoke 72 (see FIG. 40).
A coil 720 is adhered to a lock ring 719 (see FIGS. 39, 40 and 44), and a bearing 719b is located on the back face of a lug 719a of the lock ring 719 (see FIG. 45). Then, an armature pin 712 (see FIG. 39) is inserted into an armature 724 through an armature spring 723 after inserting an armature rubber 722 into the armature pin 722 and the armature pin 722 into the bearing 719b, thus fixing the armature 724 by caulking.
The armature 724 can slide in a direction indicated by the arrow 725 with respect to the lock ring 719 against the charge force of the armature spring 723.
FIG. 45 is a plan view of the blur correction apparatus after assembly, which is seen from the backside of FIG. 39. In FIG. 45, the lock ring 719 is mounted in the base plate 71 by a known bayonet coupling technique such that notch portions 719c formed (in three places) around the outside diameter of the lock ring 719 are fitted with projections 71j formed (in three places) around the inside diameter of the base plate 71, and the lock ring 719 is pressed in the base plate 71 and rotated in the clockwise direction to prevent the lock ring 719 from getting out of the base plate 71.
Thus the lock ring 719 can rotate about the optical axis with respect to the base plate 71. However, the notch portions 719c and the projections 71j would come to the same positions again while rotating the lock ring 719. To prevent the bayonet coupling from being released, a lock rubber 726 is pressed into the base plate 71 (see FIGS. 39 and 45). The lock rubber 726 restricts the rotation of the lock ring 719 within an angle xcex8 of the notch portion 719d (see FIG. 45).
The permanent magnet (locking magnet) 718 is also provided for a locking yoke 727 (see FIG. 39) as a magnetic material, which is mounted on the locking yoke 727 by fitting pins 71k of the base plate 71 in holes 727a (provided in two places) of the locking yoke 727 (see FIG. 45) and screwing holes 727b and 71n (both provided in two places).
The permanent magnet 718 on the base plate 71, the permanent magnet 718 on the locking yoke 727, the second yoke 72 and the locking yoke 727 form a known closed magnetic circuit.
The lock rubber 726 is screwed to the locking yoke 727 and prevented from coming off. The locking yoke 727 is not shown in FIG. 45 for the sake of easy understanding of the above description.
A lock spring 728, which is inserted between a hook 719e of the lock ring 719 and a hook 71m of the base plate 71 (see FIG. 45), forces the lock ring 719 to rotate in the clockwise direction. An absorbing coil 730 is inserted into an absorbing yoke 729 (see FIGS. 39 and 45) and screwed in a hole 729 of the base plate 71.
The terminal of the coil 720 and the terminal of the absorbing coil 730 are formed into a twisted pair, e.g., of tetrone coated four-twisted wires, and soldered to a basic portion 716d of the flexible substrate 716.
The above-described mechanisms in the blur correction apparatus are roughly divided into three means, i.e., a correction means for offsetting the optical axis, a means for supporting the correction means and a means for engaging the correction means.
The correction means is made up of the lens 74, the support frame 75, the coils 76p and 76y, the IREDs 77p and 77y, the position detecting elements 78y and 78y, the ICs 731p and 731y, the support balls 79a and 79b, the charge spring 710 and the support shaft 711. The support means is constituted of the base plate 71, the second yoke 72, the permanent magnets 73 and the first yoke 712. The lock means is constituted of the permanent magnet 718, the lock ring 719, the coil 720, the armature shaft 721, the armature rubber 722, the armature spring 723, the armature 724, the lock rubber 726, the yoke 727, the lock spring 728, the absorbing yoke 729 and the absorbing coil 730.
Among such elements constituting the correction means, the lens 74 and the support frame 75 form a correction optical system; the PSDs 78p and 78y, the ICs 731p and 731y, and the IREDs 77p and 77y form a position detecting means; and the coils 76p and 76y, the second yoke 72, the permanent magnets 73 and the first yoke 712 form a driving means. The correction means is constructed by the combination of the correction optical system, the position detecting means and the driving means for driving the correction optical system.
A blur prevention system (blur prevention apparatus) is then constituted of the blur correction apparatus, the vibration detecting means (see FIG. 38) and a calculation means to be shown below in FIG. 46.
The ICs 731p and 731y on the hard substrate 715 are used for amplifying outputs of the position detecting elements 78p and 78y, respectively, and internal arrangements thereof are shown in FIG. 46 (since the ICs 731p and 731y have the same circuit structure, FIG. 46 shows only the IC 731p).
In FIG. 46, current-voltage conversion amplifiers 731ap and 731bp convert photoelectric currents 78i1p and 78i2p, caused by the light-projecting element 77p and flowing through the position detecting element 78p (consisting of resistors R1 and R2), into respective voltages. A differential amplifier 731cp calculates and amplifies a difference between outputs of the current-voltage conversion amplifiers 731ap and 731bp. 
As discussed above, although light emitted from the light-projecting elements 77p and 77y is incident on the position detecting elements 78p and 78y via the slits 75ap and 75ay, when the support frame 75 moves on the plane perpendicular to the optical axis, the incident positions on the position detecting elements 78p and 78y vary.
The position detecting element 78y is sensitive to light in a direction indicated by the arrow 78ap (see FIG. 39). The slit 75ap has a shape to expand a beam of light in a direction perpendicular to that indicated by the arrow 78ap (i.e., to expand it in a direction indicated by the arrow 78ay) and focus the beam in the direction indicated by the arrow 78ap. Therefore, only the movement of the support frame 75 in a direction indicated by the arrow 713p changes a balance between the photoelectric currents 78i1p and 78i2p in the position detecting element 78p, and the differential amplifier 731cp sends an output in accordance with the movement of the support frame 75 in the direction of the arrow 731p. 
On the other hand, since the position detecting element 78y has detection sensitivity in the direction of the arrow 78ay (see FIG. 39) and the slit 75y has a shape extending in a direction perpendicular to that of the arrow 78ay (i.e., extending in the direction of the arrow 78ap), the position detecting element 78y changes its output only when the support frame 75 moves in the direction indicated by the arrow 713y. 
An addition amplifier 31dp calculates the sum of outputs of the current-voltage conversion amplifiers 731ap and 731bp (the total sum of light receiving amounts in the position detecting element 78p) to output a signal. A driving amplifier 731ep receives the signal and drives the light-projecting element 77p in accordance with the signal.
The light-projecting element 77p is very sensitive to temperature: its light projecting amount, and hence the absolute magnitude of the photoelectric currents 78i1p and 78i2p (78i1p+78i2p) in the position detecting element 78p, changes unstably. For this reason, the output of the differential amplifier 831cp (78i1pxe2x88x9278i2p) indicative of the position of the support frame 75 is also varied.
However, the light-projecting element 77p can be controlled by the driving circuit such that the total sum of light receiving amounts is kept constant, thereby preventing output variations in the differential amplifier 731cp. 
The coils 76p and 76y shown in FIG. 39 are located inside the closed magnetic circuit consisting of the permanent magnets 73, the first yoke 712 and the second yoke 72. The support frame 75 is driven in the direction of the arrow 713p by permitting current to flow through the coil 76p (known Fleming""s left-hand rule) and in the direction of the arrow 713y by permitting current to flow through the coil 76y. 
In general, when outputs of the position detecting elements 78p and 78y are amplified at the ICs 731p and 731y and the coils 76p and 76y are driven in accordance with the outputs, the support frame 75 is driven to vary outputs of the position detecting elements 78y and 78y. 
If the driving directions (polarities) of the coils 76p and 76y are set such that outputs of the position detecting elements 78p and 78y become small (negative feedback), the support frame 75 will be stabilized by the driving force of the coils 76p and 76y in a position in which the outputs of the position detecting elements 78p and 78y almost become zero.
Such a driving technique for performing driving via a negative feedback of the position detection outputs is called a position control technique. For example, if an external target value (e.g., an angle of hand vibration signal) is mixed in the ICs 731p and 731y, the support frame 75 will be driven very faithfully in accordance with the target value.
In actual practice, outputs of the differential amplifiers 731cp and 731cy are sent to a main substrate, not shown, via the flexible substrate 716, subjected to an analog/digital conversion (A/D conversion), and taken into a microcomputer.
In the microcomputer, the outputs are compared with the target value (angle of hand vibration signal) and amplified properly, and subjected to phase lead compensation (for more stable position control) by a known digital filtering technique. Then the outputs are passed through the flexible substrate 716 again and input to an IC 732 (for driving the coils 76p and 76y). The IC 732 performs a known PWM (pulse width modulation) driving of the coils 76p and 76y on the basis of the input signal to drive the support frame 75.
As discussed above, the support frame 75 is slidable in the directions of the arrows 713p and 713y, and is kept in a stable position by the above position control technique. However, it is difficult for consumer optical equipment such as cameras to control the support frame 75 constantly because of a need to avoid extra power consumption.
Further, the support frame 75 can move freely on the plane perpendicular to the optical axis in an uncontrolled state. It is therefore necessary to avoid generation of collision sound or damage to stroke ends.
As shown in FIGS. 45, 46, 47A and 47B, three radial projections 75f are provided on the backside of the support frame 75, with the tips of the projections 75f being fitted with an inner edge surface 719g of the lock ring 719 in a manner shown in FIGS. 47A and 47B. Thus the support frame 75 is restricted in all directions with respect to the base plate 71.
FIGS. 47A and 47B are plan views showing an operational relationship between the lock ring 719 and the support 75, in which only the main parts are extracted from the plan view of FIG. 45. For the sake of easy understanding of the description, the layout is somewhat different from that of an actual assembly. For the same purpose, cam portions 719f (in three places and shown in FIGS. 40 and 44) of the lock ring 719 are shown though they are not provided all over the bus line of the cylinder of the lock ring 719 and are actually not seen from the direction of FIG. 45.
As shown in FIG. 40, the coil 720 (with four-twisted-wire outgoing lines 720a, that are passed through the outer edge of the lock ring 719 via a flexible substrate or the like, not shown, and connected from the terminal 719h to the terminal 716e on the basic portion 716d of the flexible substrate 716) is located inside the closed magnetic circuit between the permanent magnets 718. A flow of current causes the coil 720 to create a torque to rotate the lock ring 719 about the optical axis.
The driving of the coil 720 is also controlled by a command signal input from an unillustrated microcomputer through the flexible substrate 716 to a driving IC 733 on the hard substrate 715. In other words, the IC 733 performs PWM driving of the coil 720.
In FIG. 47A, the winding direction of the coil 720 is set such that a counterclockwise torque is allowed on the lock ring 719 when the coil 720 is energized. Thus the lock ring 719 can rotate in the counterclockwise direction against the spring force of the lock spring 728.
Before the coil 720 is energized, the lock spring 728 forces the lock ring 719 to be in stable contact with the lock rubber 726.
When the lock ring 719 rotates, the armature 724 strikes the absorbing yoke 729. At this time, the armature spring 723 is compressed to equalize the position between the absorbing yoke 729 and the armature 724. After that, the lock ring 719 stops rotating as shown in FIG. 47B.
FIG. 48 is a timing chart showing a driving operation of the lock ring.
In FIG. 48, the coil 720 is energized (PWM driving as indicated by 720b) at a timing indicated by the arrow 719i, and simultaneously, the absorbing magnet 730 is energized (730a). Consequently, the armature 724 strikes the observing yoke 729 and is absorbed by the observing yoke 729 after equalization.
When stopping to the energizing of the coil 720 at point 720c, the lock spring 728 tends to force the lock ring 719 to rotate in the clockwise direction, but the rotation of the lock ring 719 is restricted because the armature 724 is absorbed by the observing yoke 729 in the manner described above. Since the projections 75f of the support frame 75 are respectively located in positions opposite to cams 719f (the cams 719 rotate and come to the positions), the support frame 75 can move the distance in a clearance between the projection 75f and the cam 719f. 
Thus the support frame 75 moves downward in a direction of gravity G (see FIG. 47B), but never falls because the support frame 75 also enters a controlled state at the point indicated by the arrow 719i in FIG. 48.
Although the support frame 75 is restricted and retained by the inner edge of the lock ring 719, it actually has play corresponding to that in the fit between projections 75f and the inner edge wall 719g. In other words, the support frame 75 moves downward by an amount of the play in the direction of gravity G and deviates its center from that of the base plate 71. For this reason, the support frame 75 under control is shifted to the center of the base plate 71 (light axis center) gently in a time period from the point 719i, e.g., one second.
Such slow shifting is needed because the photographer may find an image blur through the correction lens 74 and feel uncomfortable when the support frame 75 is shifted rapidly, and there is a need to prevent deterioration of the image due to shift of the support frame 75 even when an exposure operation is performed during this period (e.g., the support frame 75 is shifted by 5 xcexcm for xe2x85x9 sec.).
More specifically, outputs of the position detecting elements 78p and 78y at the point 719i are memorized as target values. The support frame 75 is controlled on the basis of the target values and shifted one second to the light axis center as a target value previously set (see 75g in FIG. 48).
After that, the lock ring 719 is rotated (to enter an unlock state), and the support frame 75 is driven to start a vibration preventing operation on the basis of the target value from the vibration detecting means (along with the operation for shifting the center position of the support frame 75).
To finish the vibration prevention, the vibration prevention system is turned off at the point 719i so that the target value from the vibration detecting means cannot be input to the correction driving means for driving the correction means, thereby controlling the support frame 75 to stop in the center position. When stopping the energizing of the absorbing coil 730 at this timing (730b), the armature 724 is released from the absorbing force of the absorbing yoke 729, and the lock ring 719 is rotated clockwise by the lock spring 728 to return to the state shown in FIG. 47A. Since the lock ring 719 strikes the lock rubber 726 and the rotation thereof is restricted by the lock rubber 726, the collision sound of the lock ring 719 is reduced at the end of the rotation.
After that (e.g., after 20 msec.), the correction driving means under control is released, and the timing chart of FIG. 48 is ended.
FIGS. 49 to 51 show a blur prevention system, in which FIG. 49 is a block diagram showing a general structure, and FIGS. 50 and 51 are block diagrams showing detailed arrangements of respective means. More specifically, means lined up in the upper row of FIG. 49 are shown in FIG. 50 and means lined up in the lower row of FIG. 49 are shown in FIG. 51. To clarify the connections between means on the upper side and means on the lower side, symbols a to g are given to respective signal lines.
In these drawings, a vibration detecting means 91 corresponds to the vibration detecting means 83p and 83y in FIG. 38, which is constituted of a vibration detection sensor such as a vibration gyro for detecting an angular velocity, and a sensor output calculating means for cutting a DC component of an output of the vibration detection sensor and integrating the output to achieve an angular displacement.
The angular displacement signal from the vibration detecting means 91 is input to a target value setting means 92. The target value setting means 92 is constituted of a variable differential amplifier 92a and a sample hold circuit 92b as shown in FIG. 51. Since the sample hold circuit 92b is normally in a sampling state, signals at both inputs of the variable differential amplifier 92a are equal to each other at all times and an output thereof becomes zero. However, when the sample hold circuit 92b enters a hold state in accordance with an output of a delay means 93 to be described later, the variable differential amplifier 92a starts outputting in succession from zero at that time.
The amplification factor of the variable differential amplifier 92a can vary according to the output of a blur preventing sensitivity setting means 94. Although the target value signal from the target value setting means 92 is a target value (command signal) which a correction means 910 can follow, since the correction amount of the image surface (blur preventing sensitivity) to the driving amount of the correction means 910 varies according to optical characteristics based on changes in focal point such as zooming and focusing, changes in blur preventing sensitivity must be compensated. This is the reason the amplification factor of the variable differential amplifier 92a is variable.
As shown in FIG. 50, the blur preventing sensitivity setting means 94 receives zooming focal-distance information from a zooming information output means 95 and focusing focal-distance information based on distance measuring information of an exposure preparing means 96. The blur preventing sensitivity is calculated on the basis of the information or blur prevention sensitivity information previously set is extracted on the basis of the above information to change the amplification factor of the variable differential amplifier 92a in the target value setting means 92.
A correction driving means 97 corresponds to the ICs 731p, 731y and 732 on the hard substrate 715 of FIG. 39, to which the target value from the target value setting means 92 is input as a command signal.
A correction start up means 98 is a switch for controlling connections of the IC 732 on the hard substrate 75 of FIG. 39 to the coils 76p and 76y in the correction means 910. As shown in FIG. 51, a switch 98a is normally connected to a terminal 98c so that both ends of each of the coils 76p and 76y will be short-circuited. When a signal is input from a logical multiplying means 99, the switch 98a is connected to a terminal 98b so that the correction means 910 can enter the controlled state (blur correction has not been performed yet, but the coils 76p and 76y are supplied with power to stabilize the correction means 910 in a position in which the signals from the position detecting elements 78p and 78y almost become zero). At this time, the output signal from the logical multiplying means 99 is also input to an engagement means 914 to release the correction means 910 from the engagement.
The correction means 910 inputs position signals from its position detecting elements 78p and 78y to the correction driving means 97 so that the position control can be performed in the manner described above.
When both an SW1 signal caused by half switching on a release button of a releasing means 911 and an output signal from a blur prevention switching means 912 are input, the logical multiplying means 99 outputs a signal from an AND gate 99a (see FIG. 50) as an element thereof. As shown in FIG. 51, when a blur prevention switch in the blur prevention switching means 912 is operated and the release button is half switched on by the photographer, the correction means 910 is released from the engagement and enters the controlled state.
As shown in FIGS. 49 and 50, the SW1 signal caused by half switching on the release button of the release means 911 is input to the exposure preparing means 96 to perform photometry, measure a distance and drive lens focusing. Thus focusing information is obtained and input to the blur preventing sensitivity setting means 94.
The delay means 93 receives the output signal from the logical multiplying means 99, and outputs it after one second to make the target value setting means 92 output the target value signal in the manner described above.
As is not shown here, the vibration detecting means 91 is started in synchronism with the SW1 signal caused by half switching on the release means 911. As discussed above, sensor output calculation via a large time-constant circuit such as an integrator takes time to some extent from starting until the output is stabilized.
The delay means 93 serves to output the target value signal after waiting to stabilize the output of the vibration detecting means 91. The delay means 93 starts blur prevention after the output of the vibration detecting means 91 is stabilized.
An exposure means 913 performs a mirror-up operation in response to input of an SW2 signal caused by a full switching (complete pushing) on operation of the releasing means 911, opens and closes a shutter at a shutter speed determined based on a photometric value of the exposure preparing means 96 to control exposure, and performs a mirror-down operation to finish all the photographing operations.
After the end of the photographing operations, when the photographer releases the releasing means 911 to turn off the SW1 signal, the logical multiplying means 99 stops outputting the signal, the sample hold circuit 92a in the target value setting means 92 enters a sampling state, and the output of the variable differential amplifier 92a becomes zero. Thus the correction means 910 returns to the controlled state in which correction driving is stopped.
When the output of the logical multiplying means 99 is turned off, the engagement means 914 engages the correction means 910. After that, the switch 98a in the correction driving means 98 is connected to the terminal 98c to inhibit the correction means 910 from being controlled.
A timer, not shown, controls the vibration detecting means 91 to continue its operation for a fixed time period (e.g., five seconds) after the operation of the releasing means 911 has been stopped. The photographer often performs another release operation continuously after stopping the last release operation. It is therefore necessary to prevent the vibration detecting means 91 from being started up every time and hence to reduce waiting or stand-by time before stabilization. This is the reason the vibration detecting means 91 is set to continue its operation for a fixed period of time. When the vibration detecting means 91 has already been started up, the vibration detecting means 91 sends the delay means 93 a start-settled signal to reduce the delay time.
FIG. 52 is a flowchart showing a sequence of operating steps in a case where a microcomputer processes the above operations. The description will be made below in brief.
When power is connected to a camera, the microcomputer checks the status of the blur prevention switch. If the switch is on-state, it is next checked whether or not the SW1 signal caused by half switching on the releasing means 911 is generated (steps #5001 to #5002). If the SW1 signal has been generated, an internal timer is started (step #5003). Next, to enable photometry, distance measuring and vibration detection start, and the correction means 910 to perform blur prevention control, the correction means 910 is released from the engagement (step #5004).
It is then checked whether or not time counted by the timer has reached a predetermined time t1. If not reached, this step is repeated until it reaches the time t1 (step #5005). As discussed above, this processing step is to wait until the sensor output is stabilized. When the predetermined time t1 has elapsed, the correction means 910 is driven on the basis of a target value signal to start blur prevention control (step #5006).
It is next checked whether or not the SW2 signal caused by full switching on the releasing means 911 is generated (step #5007). If not generated, it is checked again whether or not the SW1 signal is generated, and if even the SW1 signal has not been generated (i.e., if NO in step #5008), the blur prevention control is stopped and the correction means 910 is engaged in a predetermined position (steps #5011 to #5012).
When the SW2 signal is not generated but the SW1 has already been generated, a loop of operating steps #5007xe2x86x92#5008xe2x86x92#5007 is repeated. During this repetition, if the SW2 signal is generated due to full switching on of the releasing means 911 (i.e., if YES in step #5007), a film is exposed (step #5009). A state of the SW1 signal is then checked (step #5010), and if the SW1 signal is no longer generated, the blur prevention control is stopped and the correction means 910 is engaged in a predetermined position (steps #5011 to #5012).
When the above operating steps are completed, the timer is restarted after reset once (#5013), and it is checked whether or not the SW1 signal is generated within a predetermined time period (five seconds in this example) (loop of steps #5014xe2x86x92#5015xe2x86x92#5014). If the SW1 signal is generated within five seconds after the blur prevention control has been stopped (i.e., if YES in step #5015), photometry and distance-measuring operations are performed and the correction means 910 is released from the engagement (step #5016). Since vibration detection continues, the correction means 910 under control is driven at once on the basis of the target value signal (step #5006), and the same operating steps as described above are repeated after that.
As described above, such an operation allows the photographer to perform another release operation continuously after stopping the last release operation without restarting the vibration detecting means 91 and waiting for stabilization of the output each time a release operation is performed.
On the other hand, if the SW1 signal has not been generated within five seconds after the blur prevention control has been stopped (i.e., if YES in step #5014), vibration detection is stopped (i.e., driving of the vibration detecting means 91 is stopped) (step #5017). Then, the operation-returns to step #5001 and the blur prevention switch enters the On-waiting state.
In general, deterioration of an image due to hand vibration becomes large when a focal distance of the camera is long (e.g., 200 mm or tele-operate zooming in the case of a camera with a zoom lens) or when the shutter speed is slow (e.g., xe2x85x9 sec. exposure time).
The magnitude of hand vibration (hand vibration amount or hand vibration speed) is also undefined, and it is different between the time the photographer takes a posture with the camera aiming at a photographic object and the time the photographer operates an operation element of the camera.
Now, assume that the photographer takes a posture with a camera 61 such as one shown in FIG. 53 aiming at a photographic object, and strongly presses a release button 61a in a direction indicated by the arrow 62 for taking a picture.
This pressing force causes the camera 61 to shift in a direction of the arrow 63 and rotate in a direction of the arrow 64. FIG. 54 shows a vibration waveform recorded in this situation;
In FIG. 54, the abscissa indicates time (elapsed time since the photographer began to take a posture with the camera) and the ordinate indicates hand vibration amount. SW1 is a signal for photometry and distance measuring, which is caused by half switching on the release button 61a, and SW2 is a signal for exposure, which is caused by full switching on the release button 61a. The exposure operation is started a predetermined time after the SW2 signal is generated. A fixed time period (response delay time) existing between the time the SW2 signal is generated and the time actual exposure is performed is described as xe2x80x9crelease time lagxe2x80x9d and represented by Tr.
As is apparent from a vibration waveform 51, a large vibration 51a appears after generation of the SW2 signal. This is caused by a vibration of the camera due to a strong pressing force exerted on the release button 61a. Since the SW1 signal is supplied by half switching on the release button, the photographer pays attention to degree of the pressing force (to prevent the SW2 signal from being generated by strongly pressing the release button), and a considerable increase in hand vibration amount does not appear during this half switching-on operation.
As discussed above, a release operation for exposure can cause a large vibration. Even if hand vibration, for example, caused when the photographer takes a position with a camera set in the short focal distance (wide-operate zooming), does not effect an image very much, deterioration of the image or an image blur caused by the release operation causes a problem.
Next, assume that blur correction is performed using the above blur prevention system.
FIG. 55A is a graph in which an effect of the correction means is overlapped on the hand vibration waveform 51 in FIG. 54, indicating its driving waveform by a curve 41. The correction-means starts driving at the time of generation of the SW1 signal, and faithfully follows changes in hand vibration to be offset. Since the correction stroke of the correction means is restricted mechanically (within a blur correcting region 43), the correction means reaches the correction stroke end at a point indicated by the arrow 41a. For this reason, a blur due to a large vibration after generation of the SW2 signal cannot be corrected any longer.
FIG. 55B is a graph showing a difference between the actual hand vibration waveform 51 of FIG. 55A and the correction means driving waveform 41, i.e., showing a waveform 42 indicative of a blur correction residual amount. The waveform 42 is kept flat without any blur correction residue from the time the SW1 signal is generated (because there is no change in blur correction residue even when a photographing operation is performed during this period). After full switching on of the release button 61a, i.e., after generating the SW2 signal, the correction means fully operates to correct a large blur but stops the blur correction when it has reached the stroke end. Thus a blur correction residual amount X0 appears during this period as shown in FIG. 55B.
Unfortunately, most cameras are designed to begin an exposure operation with a delay (release time lag Tr) after generation of the SW2 signal. In a photographing operation using such a camera, a large blur is created at this time (the camera is largely displaced during the time period from the time the SW2 signal is generated until exposure is started). In many cases, the correction means reaches the stroke end during this period and blur correction cannot be performed any longer at the actual exposure time.
In addition to the system in which blur correction is started at generation of the SW1 signal, another system designed to start blur correction at the time of generation of the SW2 signal has also been proposed.
However, even if the blur correction has an initial position at the time of generation of the SW2 signal, since a large blur is caused after the SW2 signal is generated, it would be difficult to prevent such an accident as the correction means reaches the correction stroke end during the exposure time.
In one aspect of the present invention, there is provided an apparatus for an image blur correction device applied to a camera, which comprises an operation means for starting an image blur correction operation of the image blur correction device in accordance with predetermined actions to start a photographing operation of the camera; and a variable means for causing the operation means to change, in accordance with either the exposure time in the photographing operation of the camera or the focal distance in the photographing operation of the camera, timing of the image blur correction device to start the image blur correction operation in accordance with the predetermined actions to start the photographing operation, wherein the timing of the image blur correction device to start the image blur correction operation is changed in correspondence to a degree of influence of a camera fluctuation (the degree varying according to the exposure time or the focal distance) caused by the predetermined actions to start the photographing operation of the camera.
In another aspect of the present invention, there is provided an apparatus for an image blur correction device applied to a camera, which comprises an operation means for starting an image blur correction operation of the image blur correction device in accordance with predetermined actions to start a photographing operation of the camera; and a variable means for setting a blur correction operation starting timing for the operation means to switch controls of the operation means between a first operation starting control to start the image blur correction operation at first timing in accordance with the predetermined actions to start the photographing operation and a second operation starting control to start it at second timing different from the first timing, the timing of starting the image blur correction operation being set to start the image blur correction operation prior to start of actual exposure irrespective of the first operation starting control or the second operation starting control, wherein the variable means switches the timings of starting the image blur correction operation at least between the first and second timings in accordance with various conditions so that the exposure operation of the camera can be started in the condition that the image blur correction has already been performed irrespective of the first timing or the second timing.
In another aspect of the present invention, there is provided a camera comprising a release operation unit; an operation means for starting an exposure operation in accordance with a predetermined action of the release operation unit and starting actual exposure with a release time lag after the predetermined action; and a variable means for varying the release time lag in accordance with at least either the exposure time in a photographing operation of the camera or the focal distance in the photographing operation of the camera, wherein the release time lag is changed in correspondence to a degree of influence of a camera fluctuation (the degree varying according to the exposure time or the focal distance) caused by predetermined actions to start the photographing operation of the camera.
In another aspect of the present invention, there is provided an apparatus for an image blur correction device applied to a camera with an operation unit performing a first operation for starting a photographing preparing operation and a second operation for starting a photographing operation, which comprises a determination means for determining a difference in operate time between the first operation and the second operation; and a control means, in accordance with the determination by the determination means, for carrying out, corresponding to the difference determined by the determination means, (1) determination of whether the image blur correction device is in an operating state or non-operating state, (2) determination of whether to cause the image blur correction device to perform the image blur correction operation in a first manner or a second manner different from the first manner, or (3) control of predetermined indications related to the image blur or (4) varying a time from the second action to a start of actual exposure, wherein it is determined how large a camera fluctuation is on the basis of the difference in operate time between the first operation and the second operation, the camera fluctuation being caused by predetermined actions to start the photographing operation of the camera (and degree of the fluctuation varying depending on the difference in operate time between the first operation and the second operation), such that the release time lag is changed in accordance with the determination.